1. Field of Invention
This invention relates to a system and a method for locating vehicles, and more particularly to a system and a method which use a data network, such as the Internet, to monitor vehicle movements and to transmit travel-related information to vehicles.
2. Description of the Related Art
The global position system ("GPS") is used for obtaining position information. A GPS receiver receives ranging signals from several GPS satellites, and triangulates these received ranging signals to obtain the measured position of the receiver. A more detailed discussion of a GPS receiver is found in U.S. patent application ("Copending Application"), Ser. No. 08/779,698, entitled "Structure of An Efficient Global Positioning System Receiver," attorney docket no. M-4578, assigned to the present assignee. The Copending Application is hereby incorporated by reference.
One application of GPS is vehicle location. A conventional vehicle locating system typically includes one or more ground stations and many mobile units installed on the vehicles. In such a system, each mobile unit is equipped with a GPS receiver and a wireless transmitter. Using the GPS receiver, a mobile unit determines the position of the vehicle and then transmits the position directly to a ground station. The ground station receives the positions of all vehicles, and displays these positions on a digital map on a display device. The ground station of a conventional vehicle locating system normally also includes a map database search system, a media reader (e.g., a CD-ROM drive) and media (e.g., CD-ROMs) that store digital maps and travel-related information. Using the stored digital maps and positioning information received from the GPS satellites, the operator of the ground station can determine a present position for the vehicle.
The conventional vehicle locating system described above has several limitations. First, a direct wireless communication link between a vehicle and the ground station is required. Such a communication link is expensive, especially for long-distance communication. Further, special software must be installed on each ground station which adds to time and money costs. Thus a conventional vehicle locating system is impractical for a small company that has only a small number of vehicles.
Secondly, conventional vehicle location systems are not standardized. Typically, a company using a vehicle locating system must devise its own map software and create its own digital maps. The amount of information that is available on a conventional vehicle locating system is limited by the capacity of the storage system. In addition, information in such a system is often updated by creating a new CD-ROM. Statistical information, such as traffic condition and traffic patterns of the routes, is typically not available because each operation is independent and isolated from the other.